1. Field of the Invention
The present invention generally relates to a semiconductor device manufacturing method, a semiconductor device, and a semiconductor device unit, and particularly to a manufacturing method of a semiconductor device having a structure in which a lid is implemented on a semiconductor chip, a semiconductor device, and a semiconductor device unit.
2. Description of the Related Art
With the high-level densification of the semiconductor device in recent years, there is a growing tendency towards an increase in heat generated by the semiconductor chip. In response, a lid is implemented on the semiconductor chip in order to efficiently cool the semiconductor chip.
On the other hand, high reliability is also demanded in a semiconductor device. Thus, the desired semiconductor device is a highly reliable semiconductor device that is provided with a lid but does not suffer stress or separation in between said lid and the semiconductor chip.
The semiconductor of the BGA (Ball Grid Array) type having a structure in which a semiconductor chip is mounted on a substrate and external terminals such as solder balls are implemented on the surface opposite the surface that accommodates the semiconductor chip, is well-know in the conventional art. Also, in response to the increase in the heat generation of the semiconductor chip due to the speed-up and high-level densification of the semiconductor chip, a semiconductor device with a lid for efficient thermal dissipation implemented on the upper portion of the semiconductor chip is provided in the conventional art.
FIG. 1 and FIG. 2 show the above-described semiconductor device according to the conventional art. The semiconductor device 1A shown in FIG. 1 has a semiconductor chip 2 mounted on the upper surface of a multi-layered resin substrate 3 and solder balls 4, which are the external terminals, implemented on the lower surface of the substrate 3.
The semiconductor chip 2 is provided with bumps 6 and is bonded to the substrate 3 through flip chip bonding. Also, in order to strengthen the bonding between the semiconductor chip 2 and the substrate 3, an under fill material 7 is placed in between the semiconductor chip 2 and the substrate 3.
Lid 5A is, for example, made of metal, which has high thermal conductivity. In the conventional art, this lid 5A is bonded directly onto the upper surface of the semiconductor chip 2 using bonding material 8.
On the other hand, the semiconductor device 1B shown in FIG. 2 has a lid 5B with a protrusion 9 at its center portion. By providing the protrusion 9 on the lid 5B, the distance between the substrate 3 and the lid 5B can be augmented so that other electronic components such as a condenser (not shown in the drawing) can be implemented between the substrate 3 and the lid 5B.
Also, in the semiconductor device 1B shown in FIG. 2, a frame 10, supporting the lid 5B, is placed on the outer perimeter of the substrate 3. By providing the frame 10, the lid receives support not only from the semiconductor chip 2 but also from this frame 10 so that the load applied to the semiconductor chip can be reduced.
As mentioned above, the substrate 3 forming the semiconductor device 1A and 1B is a resin substrate, and the semiconductor chip 2 is made of semiconductor material such as silicon. Therefore, the coefficient of thermal expansion of the semiconductor chip 2 and the substrate 3 are different. Also, upon the flip chip bonding of the semiconductor chip 2 to the substrate 3, a heating process is performed on the bumps 6 for melting said bumps 6, and in the heating process for the flip chip bonding, the heat also ends up being applied to the semiconductor chip 2 and the substrate 3. Thus, warping occurs in the semiconductor chip 2 due to the difference in the coefficient of thermal expansion between the semiconductor chip 2 and the substrate 3.
A description of the problem arising from bonding the lid 5A to the above-described warped semiconductor chip 2 is given with reference to FIG. 3. As previously mentioned, in the conventional art the lid 5A is directly bonded to the semiconductor chip 2 using bonding material 8. Thermosetting resin is normally used as the bonding material 8, and a curing process (heating process) is performed upon the bonding.
When the curing process is performed upon the bonding of the lid 5A as described above, the semiconductor chip 2 is re-straightened from its warped form. Specifically, the semiconductor chip 2 attempts to change shape from its warped state (the state shown in FIG. 3) to the position (shape) indicated by the chain line A shown in the same drawing.
Since the bonding material 8 is placed in between the semiconductor chip 2 and the lid 5A, a compression force from the above described changing of shape of the semiconductor chip 2 works on the outer portion of the bonding material 8 (referred to as outer perimeter bonding portion 8A hereinafter). Additionally, a stretching force works on the inner portion of the bonding material 8 (referred to as inner perimeter bonding portion 8B hereinafter).
When differing forces work in the bonding material 8 upon the bonding of the semiconductor chip 2 and the lid 5A as described above, internal stress and voids may be generated therefrom. When internal stress is generated in the bonding material 8, cracks can be formed in the areas where the internal stress is generated.
Also, when voids are formed within the bonding material 8, a fissure may occur in the bonding material, or in the worst case the lid 5A may be separated from the semiconductor chip. This problem can be slightly ameliorated by making the bonding material 8 thicker; however, this also lowers the thermal conductivity of the bonding material layer 8 thereby causing a decrease in thermal dissipation efficiency with regard to the semiconductor chip 2.
The present invention has been developed in response to the above-described problems, and its object is to provide a semiconductor device manufacturing method, a semiconductor device, and a semiconductor device unit, capable of maintaining high thermal dissipation efficiency of the semiconductor device as well as improving its reliability.
To this end, the present invention resorts to each of the following measures.
First, the present invention provides a manufacturing method of a semiconductor device having a semiconductor chip mounted on a substrate, and a lid thermally connected to said semiconductor chip, the method including steps of:
implementing a stiffener, which prevents the deformation of the semiconductor chip, on the side of the semiconductor chip that accommodates the lid;
bonding the semiconductor chip accommodating the stiffener to the substrate through heating; and,
bonding the stiffener to the lid with a bonding material after bonding the semiconductor chip accommodating the stiffener to the substrate.
Preferably, the stiffener is selected from a material that has substantially the same coefficient of thermal expansion as that of the semiconductor chip.
Second, the present invention provides a semiconductor device having a semiconductor chip provided with bumps, a stiffener bonded to the semiconductor chip by a first bonding material and preventing the deformation of the semiconductor chip, a substrate on which the semiconductor chip is mounted via the bumps, and a lid bonded to said stiffener with a second bonding material, wherein the relation between the melting point of the first bonding material denoted as T1, the melting point of the bumps denoted as Tb, and the melting point of the second bonding material denoted as T2 can be described as T1 greater than Tb greater than T2.
Preferably, the stiffener is made of material that has substantially the same coefficient of thermal expansion as that of said semiconductor chip.
Third, the present invention provides a semiconductor device unit comprising a motherboard on top of which a plurality of the above semiconductor devices each having a semiconductor chip provided with bumps, a stiffener bonded to the semiconductor chip by a first bonding material and preventing the deformation of the semiconductor chip, a substrate on which the semiconductor is mounted via the bumps, and a lid bonded to said stiffener with a second bonding material is implemented.
Additionally, each of the above-described inventions produces the following effects.
According to the semiconductor device manufacturing method of the present invention, a semiconductor chip, provided with a stiffener, which prevents the deformation of the semiconductor chip, is bonded to a substrate so that warping does not occur in the semiconductor chip upon the bonding process. Thus, upon the bonding of the lid, the lid can be bonded to a stiffener that is not warped, and this prevents internal stress or voids from being generated in the bonding material placed between the lid and the stiffener. In consequence, the lid and the stiffener can be securely bonded and the reliability of the manufactured semiconductor device can be improved.
Also, since internal stress and voids are prevented from being generated in the bonding material connecting the lid and the stiffener, the bonding material can be made thinner. Thus, the thermal conductivity of the bonding material layer can be raised and the heat generated in the semiconductor chip can be efficiently transferred through the stiffener and the bonding material.
Additionally, the stiffener is selected from a material that has substantially the same coefficient of thermal expansion as that of the semiconductor chip so that deformation such as warping upon heat application can be prevented from occurring in either the stiffener or the semiconductor chip, or in both of these elements due to the difference in the thermal expansion rate between the stiffener and the semiconductor chip. In consequence, the stiffener and the lid can be securely bonded and the reliability of the manufactured semiconductor device can be improved.
Also, in the semiconductor device according to the present invention, the relation between the melting point of the first bonding material T1, the melting point of the bumps Tb, and the melting point of the second bonding material T2 is arranged to be T1 greater than Tb greater than T2; thus, the first bonding material and the bumps will not melt upon the bonding of the lid to the stiffener with the second bonding material. Also, the first bonding material will not melt upon the bonding of the semiconductor chip to the substrate via the bumps. Thus, when the semiconductor chip is bonded to the substrate and to the lid, the stiffener is securely bonded to the semiconductor chip by the first bonding material so that deformation such as warping will not occur in the semiconductor chip and the reliability of the semiconductor device can be increased.
Also, in the semiconductor device unit according to the present invention, a plurality of the semiconductor devices each having a semiconductor chip provided with bumps, a stiffener bonded to the semiconductor chip by a first bonding material and preventing the deformation of the semiconductor chip, a substrate on which the semiconductor is mounted via the bumps, and a lid bonded to said stiffener with a second bonding material are implemented on a motherboard, thereby realizing a multi-chip module with excellent heat dissipation characteristics as well as high reliability.
Additionally, in the present invention, the stiffener may be structured to have a concave portion into which a portion of the semiconductor chip is inserted. In this way, the positioning of the semiconductor chip and the stiffener can be easily determined, and the bonded area between the semiconductor chip and the stiffener is increased, thereby strengthening the bonding between these two elements.
Also, the stiffener may have chamfers formed at its corners. The chamfered portions of the stiffener are positioned at the corners of the semiconductor chip where stress is likely to be concentrated, and the stress can be prevented from concentrating on the bonding material situated in these areas. Particularly, this prevents damage such as cracks from occurring in the bonding material situated around the corners of the semiconductor chip and the lid.
Further, the stiffener may be structured to have a plurality of stiffener layers. In this way, the characteristics of the stiffener may vary for each layer so that, for example, a stiffener layer having characteristics that are close to those of the semiconductor chip can be selected for the stiffener layer implemented on the semiconductor chip side and a stiffener layer having characteristics that are close to those of the lid can be selected for the stiffener layer implemented on the lid side. Thus, the stiffener can strengthen the bonding between the semiconductor chip and the lid and deformation such as warping can be controlled.